Optical devices, such as laser rods, operate in an environment that often has a rapidly changing and highly variable thermal environment. The thermal changes can induce thermo-optical and thermo-mechanical misalignment. It is important to maintain the optical element at the correct operating temperature to reduce thermal-induced misalignment and to avoid thermal stress, while maintaining stable mechanical location.
A particular example of the importance of thermal stability is a solid state laser system which is based upon optical excitation of a laser rod. The laser rod has a characteristic optical transition at a specific wavelength. It is well known that there are a number of factors that impact the lasing efficiency, lensing effects within the laser rod and the beam quality of the emitted radiation. For example, thermal-induced lensing and birefringence is a known problem in Nd:YAG.
As the laser rod is pumped with energy from the pump source, some of the energy is converted to heat which must be removed evenly from the laser rod to avoid thermal-optical misalignment and thermal-mechanical stress. To achieve this a good and even thermal conductivity is required from the entire surface of the optical element to an efficient heat sink. However, it has proven difficult to design a mount that achieves the desired thermal transfer properties without inducing mechanical stress due to clamping of the optical device to the mount. Furthermore, expansion and contraction of the rod due to the large thermal variation during pumping accentuates any mechanical stress that may be present and induces thermal stresses that are not present in the absence of the heat load.
The prior art approaches to mounting optical elements to dissipate heat loads include the use of a pair of matching ‘V’ blocks with the laser rod sandwiched therebetween. An example of this approach is described in U.S. Pat. No. 6,754,418. Heat is extracted from one or both of the ‘V’ blocks. Another example of using a pair of ‘V’ blocks is found in United States patent application 2004/0165625 where springs are used to maintain a holding piece (upper ‘V’ block) in place to reduce the risk of damage to the optical element when thermal expansion occurs. The main disadvantage of this design is that if thermal expansion occurs which is sufficient to cause the holding piece to push away from the holder (lower ‘V’ block), thermal transfer from the holding piece to the holder will be lost on one or both sides and poor thermal stability will result.
The prior art devices fail to maintain the required level of thermal stability.